1. Field of the Invention
The present invention relates to organosilicon compounds having alkynol groups, processes for the preparation thereof, the use thereof in silicone materials crosslinkable by addition of Si-bonded hydrogen at an aliphatic carbon-carbon multiple bond, and moldings produced therefrom.
2. Background Art
Addition-crosslinking silicone materials crosslink through reaction of aliphatically unsaturated groups with Si-bonded hydrogen (hydrosilylation) in the presence of a catalyst, typically a platinum compound. After mixing of the individual components, a ready-to-use material is obtained which has a very limited pot life, or processing time, at room temperature, since the crosslinking reactions occur even at room temperature. This necessitates, on the one hand, use of the compositions rapidly following processing, and on the other hand, frequent cleaning of the storage containers, metering units, processing machines, etc., since residual material, for example that deposited through back-mixing or adhesion to equipment walls, finally gels.
Considerable attempts have therefore been made to suppress premature onset of the crosslinking reaction at room-temperature by means of “inhibitors.” Methods of lengthening the pot life of addition-crosslinking materials include the use of inhibitors which seriously reduce the activity of the platinum catalyst at room temperature. Examples include phosphorus compounds in combination With peroxides as disclosed in U.S. Pat. No. 4,329,275 and azodicarbonyl compounds as disclosed in EP-A-490 523. The action of these types of inhibitors is based on the addition of “platinum poisons”, such as nitrogen, phosphorus or sulfur compounds to the addition-crosslinking material. Although it is thus possible to considerably increase the pot life at room temperature in some cases, a disadvantageous effect on the elevated temperature crosslinking behavior is also inevitably associated with the increased pot life, i.e. the crosslinking rates at elevated temperatures also decrease considerably. The increase in crosslinking time results in higher production costs.
Another type of inhibitor comprises organic compounds or organosilicon compounds having at least one —C≡C-group as disclosed in DE-B-1 669 965. Alkynyl alcohols and alkynyloxysilanes are described therein, inter alia, as inhibitors. These inhibitors have the advantage that the crosslinking characteristics at elevated temperatures is less adversely affected as compared to the abovementioned catalyst poisons. However, even with these alkynyl inhibitors, either the pot lives as a film in air and/or in bulk, are too short, or the crosslinking rate is too slow. Moreover, since they are monomeric compounds, the inhibitors have a relatively low boiling point and hence a high vapor pressure, so that inhibitor may evaporate even during storage, thus adversely affecting the pot life. U.S. Pat. No. 5,945,475 describes the use of an alkynyl alcohol in combination with a linear siloxane which contains alkoxy groups having aliphatic triple bonds; the alkynols are reacted with siloxanes so that free hydroxyl groups are no longer present in the end product, since the alkynol bonds to the siloxane via the hydroxyl group, generating siloxanes having alkynyloxy groups. Disadvantages are that two inhibitors have to be employed, one of which is a relatively volatile monomeric alkynol having the problems described above. Furthermore, the inhibition effect of the siloxanes containing alkynyloxy groups is only very weak (cf. U.S. Pat. No. 5,945,475, comparative example 2), and as a result, the ratio of pot life or thin-film pot life at room temperature to crosslinking rate is not optimal.